Mean arterial pressure varies directly with cardiac output and total peripheral resistance. Arterial pulse pressure varies directly with stroke volume but inversely with arterial compliance.
8.
Blood flow through capillaries is regulated chiefly by contraction of arterioles (resistance vessels). The capillary endothelium is the source of NO and PGI2, which relax vascular smooth muscles.
9.
Water and small solutes move between the vascular and interstitial fluid compartments through capillary pores mainly by diffusion but also by filtration and absorption. Molecules larger than approximately 60 kD are essentially confined to the vascular compartment. Lipid-soluble substances, such as CO2 and O2, pass directly through the lipid membranes of the capillary; the rate of transfer is directly proportional to their lipid solubility. Large molecules can move across the capillary wall in vesicles by pinocytosis. The vesicles are formed from the lipid membrane of the capillaries.
10.
Capillary filtration and absorption are described by Starling’s equation:
Filtration occurs when the algebraic sum of these terms is positive; absorption occurs when it is negative.
11. Fluid and protein that have escaped from blood capillaries enter lymphatic capillaries and are transported via the lymphatic system back to the blood vascular compartment.
12.
Physical factors that influence coronary arterial blood flow are the viscosity of the blood, frictional resistance of the vessel walls, aortic pressure, and extravascular compression of the vessels within the walls of the left ventricle. Left coronary arterial blood flow is restricted during ventricular systole by extravascular compression, and the flow is greatest during diastole, when the intramyocardial vessels are not compressed. Neural regulation of coronary arterial blood flow is much less important than metabolic regulation. Activation of the cardiac sympathetic nerves constricts the coronary resistance vessels. However, the enhanced myocardial metabolism caused by the associated increase in heart rate and contractile force produces vasodilation, which overrides the direct constrictor effect of sympathetic nerve stimulation. Stimulation of the cardiac branches of the vagus nerves causes slight dilation of the coronary arterioles. A striking parallelism exists between metabolic activity of the heart and coronary arterial blood flow. A decrease in O2 supply or an increase in O2 demand apparently releases vasodilators that decrease coronary arterial resistance. Of the known factors (CO2, O2, H+ , K+ , H2O2, adenosine) that can mediate this response, KATP channels, NO, H2O2 and adenosine are the most likely candidates, although CO2, O2, and H+ cannot be ruled out.
13.
Most of the resistance vessels in the skin are under dual control of the sympathetic nervous system and local vasodilator metabolites. The AV anastomoses found in the hands, feet, and face, however, are solely under neural control. The main function of skin blood vessels is to aid in the regulation of body temperature by constricting to conserve heat and by dilating to lose heat. Skin blood vessels dilate directly and reflexively in response to heat, and they constrict directly and reflexively in response to cold.
14.
Blood flow in skeletal muscle is regulated centrally by sympathetic nerves and locally by the release of vasodilator metabolites. In persons at rest, neural
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